Increased proportion of active soil N in Breton loam under cropping systems with forages and green manures

Effect of legume-based cropping systems on nitrogen mineralization potential of Vertisol

“…Such increased No values were observed with green manuring over a continued wheat system without fertilizer addition for Black Chernozemic samples (Campbell et al, 1991). Similarly, for Gray Luvisols, legume-based rotations were associated with increased total soil N and a greater proportional increase in active N than in total soil N (Wani et al,, 1994a). Although No values differed with the cropping systems, the leaching method could underestimate the mineralizable N content in soils as soluble organic N is also leached out with the mineral N. The values for the N mineralization rate constant (k) varied between 0.021 and 0.223 w k -~, but, such differences were not statistically significant.…”

“…For these soils k values ranged from 0.04 to 1.3 w k -l, decreasing with the increasing soil depth. Wani et al (1994a) observed a slightly higher rate constant for Gray Luvisols which had received fababean material as green manuring than the one which was continuously under continuous barley. Janzen (1987) found no effect of rotation treatments on k values.…”

“…Although cereal crops benefit from biological N fixation (BNF) and the soil N-conserving effect of the preceding legume-Rhizobium symbiosis, several reports suggest non-N "rotational effects" on soil properties and successive crops (Cook, 1988;Fyson and Oaks, 1990;Wani et al, 1991). The relation between cropping systems and the quantity and quality of soil organic matter has been inferred from studies of chemical and biological soil parameters (Birch and * ICRISAT JA (1638) ** FAX no corresponding author: +9140 241239 Dougall, 1967;Campbell et al, 1991;Wani et al, 1994a). Recently, measurements of microbial biomass (McGill et al, 1986;Wani et al, 1994b), potentially mineralizable N(No) and mineralizable C (Stanford and Smith, 1972;Wani et al, 1994a) have been used to monitor biologically meaningful changes in the quantity and quality of soil organic matter.…”

“…The relation between cropping systems and the quantity and quality of soil organic matter has been inferred from studies of chemical and biological soil parameters (Birch and * ICRISAT JA (1638) ** FAX no corresponding author: +9140 241239 Dougall, 1967;Campbell et al, 1991;Wani et al, 1994a). Recently, measurements of microbial biomass (McGill et al, 1986;Wani et al, 1994b), potentially mineralizable N(No) and mineralizable C (Stanford and Smith, 1972;Wani et al, 1994a) have been used to monitor biologically meaningful changes in the quantity and quality of soil organic matter. Some increases in soil organic matter content and N mineralization potential of Gray Luvisols have been attributed to perennial forages and legumes grown in rotations with cereals (Campbell et al, 1991;Poyser et al, 1957;Wani et al, 1994a).…”

“…Recently, measurements of microbial biomass (McGill et al, 1986;Wani et al, 1994b), potentially mineralizable N(No) and mineralizable C (Stanford and Smith, 1972;Wani et al, 1994a) have been used to monitor biologically meaningful changes in the quantity and quality of soil organic matter. Some increases in soil organic matter content and N mineralization potential of Gray Luvisols have been attributed to perennial forages and legumes grown in rotations with cereals (Campbell et al, 1991;Poyser et al, 1957;Wani et al, 1994a). Similarly, some increase in total N content of Vertisol cropped with pigeonpea (PP) or cowpea (COP) in rotation with nonlegumes for 8 years were observed in India.…”